Remove ancient wp-settings.php global unsetting code

Description

// Ensure these global variables do not exist so they do not interfere with WordPress.
unset( $wp_filter, $cache_lastcommentmodified );

It used to include more variables, but they were removed when a few of us took an axe to wp-settings.php back in 3.0.

I suggest we remove both. $cache_lastcommentmodified can easily become a static variable within that function (I mean, we're dealing with pre-1.5 code here) and a lot of things would be broken if people overrode WordPress globals prior to startup, not just $wp_filter.